A computer system may have a number of nodes communicating with each other through a bus. The nodes may be individual computers, controllers for mass storage devices, or other computer apparatus. A problem arising in such a system architecture is the problem of determining which node transmits next on the bus. For example, a first node may be presently transmitting a message on the bus. Upon the conclusion of that transmission, there may be several nodes seeking to begin transmission. If more than one node begins transmission at the same time, say at the completion of the transmission of the first nodes, then a data collision will occur. The problem of determining which node transmits next on a shared, multiple access, bus is termed the "arbitration problem".
The arbitration problem may be solved by having a node test the bus in order to determine if carrier is present on the bus, and then to either begin transmitting in the absence of carrier, or if carrier is detected to initiate a backoff protocol as in the well known Ethernet or CSMA/CD (Carrier Sense Multiple Access/Collison Detect protocol). An improved solution of the arbitration problem is for a node to count a number of "quiet slots" after detecting the absence of carrier on the bus, in order to minimize the probability that a data collision will occur when the node begins transmitting, where a quiet slot is a predetermined time interval, and a fixed number of quiet slots is assigned to each node. An even further improvement in the arbitration protocol makes use of a re-assignment of the fixed number of quiet slots assigned to each node, where the re-assignment is done according to rules designed to reduce bandwidth of the bus used in counting quiet slots.
However, when a number of quiet slots is changed according to rules, a problem arises when a new node is attached to the bus. A new node will have no knowledge of the past history of the bus and so will be unable to join in the assignment of quiet slots. Further, a node may "forget" its number of assigned quiet slots through hardware failure, bus noise, voltage transient, or other unforseen events. A node having either no knowledge of the history of arbitration, or having faulty knowledge, is referred to as a "deaf node". The deaf node will then be unable to participate in the arbitration process.